modify the content of comment on submit

My aim is to get a comment with that format: title<!iiTITLE –>content

I made a filter in function.php to display correctly these comments.

I have to make one when a user submits the comment. Problem, I also use ajax. So the FORM is: `<form
id=”awpsubmit_commentform_<?php echo $id;?>”
class=”comment_form”
action=”<?php echo get_option(‘siteurl’); ?>/wp-comments-post.php”
method=”post”
onsubmit=”<?php title_filter($onsubmit);echo apply_filters(‘awp_commentform_on_submit’,$on_submit); //Leave for AWP features?>”
>`

the apply_filter is for ajax, which then redirect to wp_comments_post.php.

my filters in function.php:

global $titre;
add_filter('comment_text','comment_filter');
add_filter('pre_comment_content','ajoute_titre');
function comment_filter($content) {
$i=strpos($content,'<--!TITLE -->');
if ($i){
$title='<h3>'.substr($content,0,$i).'</h3>';
$texte=substr($content,$i+13);

}
else{
$title='<h3>'.__('Without Object','stendhal').'</h3>';
$texte=$content;
}
$content=$title.$texte;
return $content;
}

function ajoute_titre($content) {
$content=$titre.'<!--TITLE -->'.$content;
return $content;
}

function title_filter($on_submit) {
$titre = trim($_POST['titre']);
}

Og course, it doesn’t work. Some help?